1. Field of the Invention
The present invention relates to a lens device suitable for an electronic camera and a photographic camera of a portable type, and further relates to an imaging device using this lens device.
2. Description of the Related Art
Size and weight of portable cameras have been reduced. In particular, as to electronic cameras incorporated into a cell-phone and a PDA (Personal Digital Assistant), taking lenses and image sensors of a CCD type and a MOS type are downsized. In virtue of this, a size of the electronic camera itself has been rapidly reduced. Some of the downsized electronic cameras have an automatic focus function for automatically performing focus adjustment by moving the taking lens in an optical-axis direction. In Japanese Patent Laid-Open Publication No. 4-69070, it is described that a driving device for moving the taking lens in the optical-axis direction utilizes a piezoelectric device to reduce size and weight of the electronic camera.
When the automatic focus function performs the focus adjustment, it is important to accurately detect a position of the taking lens. Therefore, a camera described in Japanese Patent Laid-Open Publication No. 2003-315658, for instance, comprises a ball screw, a reflector plate and a line sensor. The ball screw is fitted to an upper end of a lens frame holding the taking lens. The reflector plate is disposed at a lower end of the lens frame. The line sensor confronts the reflector plate and is disposed in an optical-axis direction. Light emitted from a light-emitting portion of the line sensor is reflected by the reflector plate. The reflected light is received by a light-receiving portion of the line sensor to detect the position of the taking lens. Meanwhile, a rod-shaped guide member is disposed in the optical-axis direction. The guide member guides the movement of the lens frame when the lens frame is moved in the optical-axis direction.
However, such as described in the above-noted Publication No. 2003-315658, the lens frame sometimes inclines due to friction, which is caused by slide movement of the guide member and the lens frame, when moved in the optical-axis direction. At this time, in the case that the reflector plate is disposed at the lower end of the lens frame such as described in the Publication No. 2003-315658, a reflecting surface of the reflector plate also inclines in association with the inclination of the lens frame. Consequently, when the light from the light-emitting portion is reflected by the reflector plate, a reflected-light receiving position of the line sensor is shifted. Thus, there arises a problem in that it is impossible to accurately detect the position of the taking lens. Further, when the light-emitting portion of the line sensor emits the light toward the lens, excess light uninvolved in image formation reaches an imaging surface, and it is caused that image contrast is lowered and a flare occurs to muddy colors of a color picture.